One type of conventional fastener includes a pair of fastener members each having a base and a plurality of arranged, headed stems adjoining and projecting from the base. The fastener members may be releasably interengaged as shown in FIGS. 5(a) and 5(b), to fasten together two objects to which the fastener members are attached.
The fastener illustrated in FIGS. 5(a) and 5(b) includes a first fastener member 1 and a second fastener member 2, each of which is molded from a polymeric material. The first and second fastener members are provided with generally flat bases 3 and 4, respectively, and a plurality of headed stems 5 arranged on the bases in a predetermined spaced relationship. Each of the headed stems includes a stem 6 projecting generally orthogonally from the base, and a head 7 connected to the end of the stem 16. The head has a diameter at at least one location that is greater than the diameter of the stem. Each head 7 has a generally flat locking surface 8 adjacent the stem 6 and extending radially from the periphery of the stem 6, and an apex 9 at an opposite side of the locking surface 8 from the stem 6.
To interengage the fastener, the first fastener member 1 and the second fastener member 2 are opposed as shown in FIG. 5(a), so that the headed stems 5 thereof confront each other while the bases are substantially parallel to each other. When a predetermined pressure is applied to the respective bases, the heads 7 of one fastener member come into contact with and slide against, at the apexes 9 thereof, the heads 7 of the other fastener member. The stems of both fastener members resiliently deflect to allow the heads to enter the space between the adjacent stems 6 of the other fastener member, as shown in FIG. 5(b). Thus, the headed stems 5 of one fastener member are engaged at their locking surfaces 8 with the locking surfaces 8 of the other fastener member, and the first and second fastener members are thereby interengaged with each other.
In an interengaging fastener member of the type described above, the headed stems are typically arranged in a regular array of rows and columns. FIG. 6 shows a standard arrangement of headed stems E, in which the headed stems are linearly arranged along mutually perpendicular axes (labeled X and Y), and along an inclined direction (shown by a broken line) that intersects the perpendicular axes. However, regular arrangements of headed stems may allow fastener members to move relative to each other in a direction parallel to the rows or columns of the fastener members, also referred to as the shear direction. Thus, although the fastener exhibits a relatively large tensile disengagement force, it may display a low shear disengagement force, which may be undesirable.
The reason why a sufficient retaining force cannot be exerted against a force acting in the shear direction is that the headed stems are regularly arranged in columns and rows. If the headed stems are irregularly arranged, it is difficult to provide desired spaces between beaded elements when manufacturing the fastener members. In addition, an irregular arrangement may not be accurately reproducible, resulting in fluctuations in the engagement and disengagement performance of the fastener members.
In view of the foregoing, it would be desirable to provide a fastener that exhibits a satisfactory disengagement force and shear force, using headed stems in a non-random arrangement.